This invention relates to an arrangement for coupling optical fibers and, in particular, to a demountable optical fiber connector assembly and an optical fiber ferrule for use in such assembly.
In an optical connector capable of joining two single fibers of very small dimensions it is essential to provide close tolerance alignment between the ends of the two fibers in order to minimize the coupling losses. In principle, it is possible to provide as alignment reference surfaces the bare fibers themselves, but in practice this is difficult due to their extreme fragility. Instead, it is usually preferred to enclose each optical fiber in a protective cylindrical ferrule, usually made from metal. The fiber is inserted from the rear of the ferrule and secured at the front so that the axes of the fiber and ferrule are accurately concentric. Two similarly terminated fibers can then be aligned by enclosing the ferrules in a guide which has either a sliding fit or an interference fit with the ferrules. Butting is ensured by an axial spring or similar means. Various means have been proposed for ensuring the concentricity of the fiber and ferrule axes. For example, co-pending application Ser. No. 679,759, filed Apr. 23, 1976, entitled "Termination of Optical Fibers", of M. J. Phillips and A. M. Crick, describes the use of a pierced watchmakers bearing jewel mounted on the end of a ferrule with the fiber end positioned in the jewel hole. Such jewels are available as standard components with hole sizes suitable for a wide range of fiber diameters, and outside diameters maintained within very close limits. In addition, the concentricity of the jewel hole to its outside diameter is very accurately controlled.
The aforementioned optical fiber connectors employing watchmakers jewels require the jewel to have a light press fit within the bore of an accurately machined ferrule. In particular, the bore, outside diameter and concentricity of the bore to outside diameter must be maintained within limits of the order of 10.sup.-4 inches. The present invention eliminates the need for these accurate dimensions by utilizing the outside diameter of the jewel directly as the alignment reference surface.